White House spokesman Jay Carney told reporters this afternoon that Obama, who has long favored reinstating that ban but had not expressed support for a specific effort to do just that, now "actively" supports the effort by California Sen. Dianne Feinstein to craft such legislation.

The president believes it is "clear we haven't done enough" to stop the "scourge" of gun violence, the spokesman said.

According to Carney, Obama would also support legislation that closes the so-called gun show loophole that has allowed some weapons to be sold without criminal background checks of the buyers. And the president would like to see legislation that aims to ban high-capacity ammunition magazines, Carney added.

"If there is even one step we can take to save another child, or another parent, or another town, from the grief that has visited Tucson, and Aurora, and Oak Creek, and Newtown, and communities from Columbine to Blacksburg before that — then surely we have an obligation to try.

"In the coming weeks, I will use whatever power this office holds to engage my fellow citizens — from law enforcement to mental health professionals to parents and educators — in an effort aimed at preventing more tragedies like this."

Carney said that the president's now-open support for Feinstein's effort is part of Obama's promise to take action.

Monday, as The Washington Post reported, Obama "began the first serious push of his administration to attempt to reduce gun violence, directing Cabinet members to formulate a set of proposals that could include reinstating a ban on assault rifles. The effort will be led by Vice President Biden."

Meanwhile, Fox News reports that "sources close to the issue [say] the National Rifle Association — which has remained silent since the shooting, chiefly to allow for a proper period for mourning — will soon start to 'push back' against the gun-control lobby."

As correspondent Alan Greenblatt wrote for NPR.org earlier, "the federal government banned certain types of semiautomatic weapons from 1994 to 2004, along with high capacity ammunition magazines. The law specified 19 particular models that were made illegal." The law was allowed to expire.

One of the weapons used in Friday's attack, according to police, was a .223-caliber Bushmaster military-style rifle.